Recently, there are many cases, particularly in uses of electric and electronic parts, where a high flame resistance coming up to a V-0 rating of UL-94 (Underwriters' Laboratory flammability test) or the like is demanded for resins used in order to secure a safety against fire. Thus, various flame retarders have been developed and investigated.
In case of imparting such a high flame resistance to resin compositions, halogen compounds have been generally used as a flame retarder, which are used, as occasion demands, in combination with a flame retarding assistant such as antimony trioxide. However, the halogen based flame retarders have a large flame retarding effect, but free halogen gas and halogen compounds produced by decomposition of the flame retarders at the time of processing of resins may corrode surfaces of a cylinder and a die of extruders for compounding, or may corrode metallic parts, when the resin compositions are used as electric and electronic parts, to cause troubles such as contact fault or conduction fault. Also, in recent years, there is a movement to completely regulate the use of halogen-containing resins with the European countries as the center figure. Further, the addition of a flame retarding assistant such as antimony trioxide has the defect that the heat stability of resins is deteriorated when melting them at high temperatures. For such reasons, it has been desired to develop a flame retarded thermoplastic resin composition containing no halogen based flame retarder such as chlorine compound and bromine compound and containing no flame retarding assistant such as antimony oxide.
As such a flame retarded resin composition, proposed is for instance a resin composition wherein an alloy of a polycarbonate resin and a polyester resin is flame-retarded by a flame retarder other than halogen based flame retarders. Japanese Patent Publication Kokai No. 64-70555 and No. 6-192553 disclose that flame retarded resin compositions containing no chlorine or bromine atom are obtained by adding a graft copolymer, a phosphorus based flame retarder such as triaryl phosphate or oligomeric phosphate and a fluorinated polyolefin to a polycarbonate/polyalkylene terephthalate alloy. If it is attempted to impart a flame retardancy with only the use of a phosphorus based flame retarder, so-called dripping phenomenon that a burnt resin drips at the time of flaming of molded articles occurs, thus failing to pass a UL-94 rating of V-0, and accordingly it is necessary, as proposed, to add a fluorinated polyolefin in order to prevent the dripping.
These flame retarded resin compositions using phosphorus based flame retarders have the problem that since other physical properties are deteriorated if it is attempted to achieve a high level of flame resistance, it is very difficult to satisfy both the flame resistance and the physical properties such as heat resistance and mechanical strength. Also, since fluorinated polyolefins are expensive, the addition thereof leads to increase in cost of the resin compositions and, therefore, it is desirable to use it in an amount as small as possible. However, if the amount is decreased, dispersion failure of fluorinated polyolefin is easy to occur, thus there arises a trouble that the flame resistance varies depending on molding processing conditions, and if the fluorinated polyolefin is added in a large amount, there arises a trouble that the appearance of molded products is decreased or the fluidity and molding processability are deteriorated. Further, because of a growing interest in environmental problem in recent years, there is a movement to restrict also the use of fluorine-containing resins in addition to bromine and chlorine based flame retarders. For such reasons, it has been demanded to develop a method for preventing the dripping of resins at burning without adding a fluorine-containing resin.
Also, Japanese Patent Publication Kokai No. 7-26129 discloses a technolgy for flame-retarding a polycarbonate resin by adding thereto a polyphosphate flame retarder, a fluorinated polyolefin, mica, talc and the like. However, such a composition is limited in the range of utilization, because of poor fluidity and chemical resistance of the resin.